The advent of tunable visible and infrared lasers makes possible laser isotope separation, the use of which has long been attractive because of the ease with which isotopes can be spectroscopically resolved. This is in marked contrast to the conventional techniques such as gaseous diffusion and the gas centrifuge which use the small mass differences of isotopes. For heavy atoms this difference is quite small. For example, U.sup.235 and U.sup.238 differ in mass by less than 2%. Consequently these more conventional techniques can achieve only marginal enrichment of the desired isotope per step. Thus, to obtain useable isotopic enrichment (e.g. 3% of U.sup.235 in U.sup.238), the process must be repeated many times. The practical implication of this is that many stages of enrichment must be cascaded, resulting in a large scale physical installation.
Additionally, different schemes of laser isotope separation are known, which may be grouped into four catagories, as follows:
1. Selective excitation of vibrational or electronic states which subsequently chemically react to produce chemical species which can then be separated.
2. Selective excitation to molecular states, which then dissociate, followed by chemical reaction with the dissociated species, and subsequent chemical separation.
3. Photon reactions with beams of atoms or molecules to give directions of the isotopic species by photon pressure.
4. Multiphoton excitation leading to excitation of autoionizing states or photoionization of the excited species and removal by electric fields.
Of the above process, the present invention relates most closely to process 4. It differs from prior art process in the use of two-photon excitation into a bound atomic level close to the ionization limit of the atom (Rydberg level) and subsequent field ionization and removal by a moderate electric field. The method and means of this invention offer significant advantages over current methods, including process 4 above.